1. Technical Field
The present invention relates to a D/A conversion circuit, an oscillator, an electronic apparatus, and a moving object.
2. Related Art
In a case where a D/A conversion circuit that is a type of resistor-caused voltage division is formed on a semiconductor substrate, for example, along a longitudinal direction of a resistive element with a predetermined width, a plurality of MOS switches are arranged adjacent to a resistive element, at the minimum distances allowed by a layout design rule, and distances (contact pitches) in a longitudinal direction of a plurality of contacts that are provided to the resistive element in order to form a plurality of division voltage resistors that have equal resistance values are set to be constant in accordance with arrangement of the plurality of MOS switches. Thus, each of the division voltage resistors and the MOS switch can be efficiently wired and a reduced area can be realized.
On the other hand, in the D/A conversion circuit that is the type of resistor-caused voltage division, in a case where a relationship between digital data that is input and an analog voltage that is output is desired to have intentional nonlinearity, because resistance values of the division voltage resistors are not equal to each other, there occurs a need to change a contact pitch for every division voltage resistor in order to form a plurality of division voltage resistors having different resistance values on the resistive element with the predetermined width. In such a case, the plurality of MOS switches cannot be arranged at the minimum distances and an unnecessary area occurs in an arrangement area of the MOS switch. Alternatively, when the plurality of MOS switches are arranged at the minimum distances, a wiring area for connecting between each contact and each MOS switch on the resistive element increases and a reduced area is difficult to realize. Particularly, the greater a difference (a ratio) between each of the division voltage resistors, the greater a difference in distance between the contacts on the resistive element. Thus, the unnecessary area or the wiring area that is described increases.
In contrast, JP-A-2014-59620 discloses a voltage division circuit, which results from arranging a plurality of resistive elements, each of which constitutes a unit resistor, side by side in a unidirectional manner, connecting the resistive elements (the unit resistors) in parallel or in series to each other and thus forming a plurality of division voltage resistors that have different resistance value. Because, with this configuration of the division voltage resistor in the division voltage circuit, lengths in the longitudinal direction, of all resistive areas can be shortened by lengthening lengths in the transverse direction, if the configuration of the division voltage resistor is applied to a nonlinear D/A conversion circuit, a difference in contact pitch between the division voltage resistors can be reduced.
However, in the division voltage circuit disclosed in JP-A-2014-59620, because a plurality of unit resistors are arranged side by side in a unidirectional manner, an unnecessary area almost does not occur in the resistive area, but the difference in contact pitch between the division voltage resistors cannot be set to be zero. Therefore, although the configuration of the division voltage resistor is applied to the voltage division circuit, with a characteristic of the nonlinear D/A conversion circuit, an occurrence of the unnecessary area described above or an increase in the wiring area cannot be suppressed sufficiently, and, in some cases, a reduced area cannot be realized.